Recovery and reinfusion of blood lost due to surgery rather than transfusion of donor blood preserves blood bank resources and eliminates the risk of transmitting infection and of adverse reaction due to donor incompatibility. Even when the amount of blood lost does not indicate transfusion, recovery and return of shed blood can benefit the patient.
Conventionally, shed blood is collected intraoperatively from an open surgical site using a hand-held suction wand. Postoperatively, a drainage tube under controlled suction removes blood from the closed cavity. The required suction is routinely provided by vacuum pumps because of the easily regulated negative pressure they provide and their relative low cost compared to other types of pumps.
U.S. Pat. No. 3,965,896 discloses an apparatus that withdraws blood from a surgical site by vacuum, filters it, adds an anticoagulant, and delivers the admixed blood to a reservoir from which it can be reinfused into the patient. Although the filtration removes blood clots and fragments of bone and other tissue, it leaves anticoagulant, cellular debris, toxins, and irrigation fluid in the blood. These elements should preferably be removed before reinfusion. Also, withdrawal of the lighter blood components, such as plasma and white blood cells, and reinfusion of only the red blood cells helps reduce bleeding.
For these reasons, it is desirable to wash the shed blood and concentrate the red blood cells following filtration and anticoagulation. Centrifugation is a commonly applied technique for performing these tasks. A typical centrifuge bowl for this application is the so called Latham bowl, described in U.S. Pat. No. 4,300,717. Blood enters through an inlet tube into a separation chamber. Rotation of the bowl separates blood in the separation chamber into its components according to density, with the red blood cells collecting at the periphery of the bowl and the various lighter components forming concentric cylinders of successively smaller radii. As the bowl fills, the red blood cells displace the lighter components, concentrated near the center, out of the bowl through an exit port to a waste receptacle. A saline washing solution may then be added to enhance segregation of entrained lighter blood components and other undesirable elements. These bowls usually operate at about 4000 to 6000 rpm.
In a typical shed blood processing system using centrifugation for washing and concentrating red blood cells, such as is described in U.S. application Ser. No. 08/036,430, shed blood from the surgical site flows into an intermediate holding reservoir under negative pressure provided by a vacuum source. When the amount of blood in the holding reservoir has reached a desired level, the blood is drawn from the holding reservoir by a peristaltic pump, and propelled through the pump and into a centrifuge bowl. Rotation of the centrifuge bowl segregates undesirable elements and concentrates the red blood cells in the bowl. After stopping rotation of the bowl, the red blood cells are removed by operation of the peristaltic pump in reverse mode to draw the cells out of the bowl, back through the pump and into a reinfusion bag from which the red blood cells can be returned to the patient by simple gravity-fed infusion.
Several minor variations based to this approach have been disclosed. For example, the vacuum action may also draw anticoagulant into the fluid stream, as in U.S. Pat. Nos. 4,668,214 and 5,234,403. Transfer from the holding reservoir to the washing apparatus may be accomplished by gravity rather than by the action of a pump, as described in U.S. Pat. No. 5,215,519 and published PCT Application No. 89/01792. A filter may be incorporated into the system at any of several locations, as in U.S. Pat. Nos. 5,311,908 and 5,234,403.
However, in all of these systems the initial collection of shed blood and its subsequent transfer to the centrifuge bowl for processing are performed separately, using physically distinct components. Intermediate reservoirs between the patient and the centrifuge bowl are used both in filling and emptying the bowl, and the system may even employ a supplementary pump, in addition to the vacuum source used for draining the surgical site. Allowing for retrieval of the concentrated red blood cells without dismounting the bowl further requires that such a supplementary pump be bidirectional. This multiplicity of pumps and reservoirs is costly and inefficient.